1. Field of the Invention
This invention relates to alarms, particularly portable, position sensitive alarms used to warn of an intruder.
2. Description of the Prior Art
Many people find that they are not as secure when staying in a hotel or motel room as they would like to be. Although valuables usually can be removed from the room when one is not occupying it, that degree of safety is absent when one is asleep in the room at night. A real or perceived danger when staying in an unfamiliar room can cause anxiety and lessen the quality of a night's sleep and the pleasure of the stay.
One way to help protect travelers is with a portable alarm which can be actuated when someone opens a door and enters the room. Portable alarms using position sensitive switches, such as mercury switches, are well known. U.S. Pat. No. 3,710,371 to Whalen et al. discloses a portable alarm which can be activated by moving or tipping the container. The Whalen patent discloses an alarm using a battery, a mercury switch, a master arming switch, and an SCR in series with a horn mounted in a cylindrical case. The gate of the SCR is connected to a feedback loop coupled to the mercury switch. Because the SCR and horn are in series, if the SCR fails and becomes an open circuit the horn will not sound regardless of the position of the alarm.
Another shortcoming of prior art portable alarms is that their circuits often require a substantial amount of energy for powering circuit components other than the warning device, typically a buzzer or horn. For example, certain circuits may drain the battery while the alarm is armed even though the mercury switch is open. Other circuits may require electrical energy to be used for powering circuit components, other than the warning device, while the warning device is sounding its alarm. With such circuits a maximal amount of energy is not available from the battery for actuating the horn or other warning device which can lessen the effectiveness of the alarm.